1. Field of the Invention
The present invention relates to an electrostatic discharge (hereinafter abbreviated as ESD) protection semiconductor device, more particularly, to an ESD protection semiconductor device with improved robustness.
2. Description of the Prior Art
With the advancement of technology, the development of semiconductor process is ongoing. A modern chip is therefore allowed to have a plurality of various electronic circuits configured within. For example, the integrated circuits (ICs) integrated in the chip(s) can be divided into core circuits and input/output (hereinafter abbreviated as I/O) circuits, and the core circuits and the I/O circuits are respectively driven by different power supply sources with different voltages. And for receiving the externally provided power, pads for core circuits and I/O circuits are required.
However, it is found that electrostatic charges are easily transferred to the inner circuits in the chip by those pads during processes such as manufacturing, testing, packaging, and delivering, etc. The electrostatic charges impact and damage the inner circuits in the chip, and this unwanted condition is named electrostatic discharge (ESD). As products based on ICs become more delicate, they also become more vulnerable to the impacts from external environment. And thus, it is assumed that ESD is a constant threat to the modern electronics. Models related to ESD tolerance are divided into human body model (HBM) and machine model (MM). For commercial IC products, the general ESD specification is required that IC products must pass these tests, for example, MM ESD tolerance greater than 200V and HBM ESD tolerance greater than 2 kV.
Furthermore, electric fields generated during operation are often crowded between the isolation structure and the drain region of the ESD protection device. This electric field crowding effect even causes soft-leakage issue, and thus robustness of the ESD device is adversely impacted. Therefore, an improved ESD protection semiconductor device is needed to solve the aforementioned deficiency.